LSP modeling of the electron beam propagation in the nail/wire targets

Mingsheng Wei, Andrey Solodov, John Pasley, Farhat Beg and Richard Stephens

Center for Energy Research, University of California, San Diego

LLE, University of Rochester,

General Atomics, San Diego

Ti wire Target:- 12 µm kinetic electrons (underdense to critical density)- background solid density Ti(+15) with Tinitial 100 eV, electrons as

the fluid species

Grid szie:- r: 0.312 -0.615 µm- z: 0.182 - 1 µm-Time step: 0.03um

Motivations Electron beam propagation and heating of the background plasmas in method 1

- Use LSP hybrid code to simulate large scale plasma that is comparable to the real experiments. - Study the electron beam transport in the nail/wire target- Benchmark code against the experiments

* This work is supported by the U.S. Department of Energy under Contract No. DE-FG03-00ER54606, No. DE-FC02-04ER54789, and No. DE-FG02-05ER54834

This work is also partially supported by the National Center for Supercomputing Applications under grant number PHY050034T and utilizes the computer facilities in SDSC.

We aim to accurately model the nail/wire experiments

Two methods used for modeling the experiment with LSP code

Nail target, Cu2+ plasma, 20μm diameter wire

t=0.5ps (pulse center)

t=1ps

t=1ps

r =0 r =7μm r =10μm

FSC

Method 1: Hot electron beam promoted from the background electrons using the empirical scaling

Method 2: Hot electron beam produced from the laser plasma interaction

LASERpulse: Gaussian, 0.5 ps (FWHM)energy: 81 Jspot size: 16.4 µm (FWHM)intensity: 51019 W/cm2

ELECTRON BEAMconversion efficiency: 30%average energy: Th~2.23 MeV

angular spread: 34 (half-cone angle)

300 µm

50 µm

12 µm underdense plasmakinetic electrons

Laser beam launchedfrom the left boundary

- Focal spot size: r0=7.5 µm- 65 J in the focal spot- 0.5 ps (top hat profile)- I~ 7.361019 W/cm2, a0=7.4

Wire target, Cu2+ plasma, 50 μm diameter wire

t=0.5ps (pulse center) t=1ps

r =0 r =17μm r =25μm

Energetic electron beam production, propagation and heating of the background plasmas in method 2 (preliminary results)

That means properly describing the experiment as well as properly simulating the physics

Target geometryLaser pulse - including prepulse Properly generate currentAnalyze in terms of diagnostics

Preformed plasma produced by the laser prepulse has been modeled using the 2d rad hydro code h2d.

Courtesy of P. Patel at LLNL

Initial target position at z=0

Density contour in low region

high region

r=0.9 µm r=7.6 µm r=25 µm

B ~ 25 MGEr ~ 2.5 MV/µm

t = 0.5 ps t = 1.0 psc t = 1.4 ps

kinetic electron density

t = 0.5 ps t = 1.0 ps t = 1.4 ps

Background electron temperature

10% of laser energy is transferred to hot electrons which cause significant reduced heating compared to that using the excitation model. MA current is carried by hot electrons. Hot electron density drops quickly (by 10 fold) in the first 20 µm. Strong azimuthal B field and radial E field are generated on the wire surface.

Future work: Simulation for the longer wire case Including the self-consistent ionization model Analyze the simulation data in terms of diagnostics used in the experiments

t = 1.0 psc

Hot electron current vs time